<!DOCTYPE html>
<html>
 <head>
    <meta charset="utf-8">
    <title>Canvas</title>
 </head>
 <style type="text/css">
    body{margin:20px auto; padding:0; width:800px; }
    canvas{border:dashed 2px #CCC}
 </style>
 <script type="text/javascript">
    function $$(id){
        return document.getElementById(id);
    }
    function pageLoad(){
        var can = $$('can');
        var cans = can.getContext('2d');
        cans.beginPath();
        cans.arc(400,300,200,0,1.5*Math.PI,true);
        cans.strokeStyle = 'red';
        cans.lineWidth = 10;
        cans.stroke();
        cans.closePath();
    }
 </script>
<body onload="pageLoad();">
    <canvas id="can" width="800px" height="600px"></canvas>
</body>
</html>  